Diaphragm type acoustic screen



July 1, 1958 R. c. JOLFRE DIAPHRAGM TYPE! ACOUSTIC SCREEN Filed Oct. 18, 1955 ENTok 1 RENE C. Jam/e5 The present invention relates to improvements in the manufacture of a device for giving protection against infection from the breath of persons situated behind a ticket-window, enquiry-window or the like, the device being of a type similar to that which formed the subject of my prior Patent No. 2,508,265.

In Patent No. 2,508,265 referred to, the protective device is essentially constituted by a composite wall or partition formed by a transparent diaphragm of cellophane or similar material, tightly stretched on a frame and interposed between two plates of rigid, transparent and plastic material, these plates which protect the diaphragm being pierced with small holes in order to permit the passage of sound, and being separated from the said diaphragm by a space of the order of 1 cm., so as to permit the diaphragm to vibrate freely.

An improvement of the above device is also known, according to which the plates which protect the diaphragm are full plates, for example sheets of glass arranged as baffle-plates.

The two resonance chambers thus formed ensure the transmission of speech without substantial attenuation and without distortion, on condition that the surface of the diaphragm has an area not less than 800 sq. cm. for example, and that the orifices or slots in the protective plates which allow the sound to pass represent at least one-tenth of the surface area of the diaphragm.

From the acoustic point of view, it should be noted that the long waves (the hubbub of public halls) are attenuated by the device and that, in consequence, an employee situated behind a device of this kind can hear speech more easily and more clearly than in the open air.

The tightness and the acoustic qualities of the device require continuously an excellent strength together with a constant tension on the diaphragm, whatever may be the physical or other conditions to which the said diaphragm may be subjected (variations in the hygrometric state of the air, in temperature, accidental perforations, etc.).

The invention has precisely for its object to ensure that the diaphragm always retains the same condition and the same tension, whatever the physical conditions to which it may be subjected. In addition, the diaphragm retains its acoustic qualities, even when it is accidentally perforated with a number of holes.

in the accompanying drawing, Figure 1 is a front elevation of a frame of the present invention with a strip of plastic material wound thereon.

Figure 2 is a horizontal sectional view of the frame and the plastic material thereon as shown in Fig. 1.

Figure 3 is a cross-sectional view of the invention installed in a Window or like panel.

A frame 1 of rectangular, square, oval or other shape, has wound thereabout a strip 2 of cellulose or plastic material, such for example as cellophane. This strip is first wound loosely around the frame 1 but later tightened so that the windings overlap and form a jacket or atent "Flee 2 V shell on the frame. An acoustic diaphragm ,3, made of cellulose or other plastic'material, for example cellulose acetate, isa'dhe sively attached to the strip 2 mindicated at 4, and stretched on the frame at a predetermined tension.

Asshown in Fig. 3 the protective unit 3 and its frame may be inserted in an opening in a window pane or panel P where it is shielded by the transparent rigid plates 5, Shaving peripheral openings 6. i

In accordance with a first feature of the invention, the diaphragm is composed of an inert and stable material, for example of cellulose acetate.

In accordance with a further feature of the invention, a diaphragm of a given thickness is mechanically stretched with a pre-determined tension, on a frame.

The mechanical tension of the diaphragm on the frame may be obtained by coating the faces of theframe with a suitable rapid-drying adhesive which ensures almost instantaneous adhesion, for example With a rapid aqueous adhesive.

Before stretching the diaphragm on the frame, the latter may be previously covered with a sheath of a material which is absorbent for the water in the adhesive and which is composed, for example, by a strip of cellophane wound round the frame. 7

For the application of the mechanical tension, a number of methods may be employed. One of these methods is indicated below by way of example:

A sheet of cellulose acetate which is to serve as the diaphragm is placed on magnetic plates which are movable with respect to each other and on which the extremities of the membrane are retained by metallic bars which are carefully fixed by magnetic attraction on the plates; the plates are then moved apart from each other,

. thus imparting the desired tension to the sheet of cellulose acetate.

A frame, the faces of which have been coated in a suitable manner with a rapid-drying adhesive, for example an aqueous adhesive, is placed on the sheet of cellulose acetate and is also attracted by the magnetic plates.

Before the magnetic plates are de-magnetised, the diaphragm is fixed in an effective manner onto one side of the frame coated with adhesive; the frame is then held in a press arrangement of any kind and the diaphragm is then folded back, side by side in turn, onto the other faces of the frame. I

The diaphragm of cellulose acetate, mechanically stretched in this way and glued on to the frame under the conditions described above, will transmit sound" without appreciable attenuation.

In addition, the variations in temperature or in the hygrometric state of the air have no influence on the tension of a diaphragm of this kind which, even if'it is accidentally perforated, does not tear, and retains its tension and its acoustic properties.

Various modifications of detail may be made to the form of embodiment described above, in respect of the nature and of the dimensions of the material employed for the diaphragm, to the method of applying tension to the said material, etc., without thereby departing from the spirit or from the scope of the invention.

The diaphragm may also be applied to the frame by. the use of any other method, either thermal or electric (welding or other process).

What I claim is:

In a protective device for insertion in a window or like panel for protecting persons from contamination by breath Without appreciably impeding sound wave transmission and clear visibility, comprising, in combination,

a frame coated with an adhesive, a sheath of moisture absorbent material constituted by a strip of cellophane spirally wound around said frame, a transparent diaphragm composed of inert stable material resistant to change in atmospheric conditions and having acoustical transmission properties, said diaphragm being of a given thickness and mechanically stretched over the sheath and secured thereto under predetermined tension, and

7 at either side of said frame and diaphragm.

References Cited in the file of this patent UNITED STATES PATENTS Jolfre May 16, 1950 Matheson et a1. Mar. 20, 1956 

